Spectacle lens for a display device that can be fitted on the head of a user and generates an image, and display device with such a spectacle lens

ABSTRACT

A spectacle lens for a display device can be fitted on the head of a user and generate an image. The spectacle lens includes a curved front and/or side, wherein a light guiding channel which is suitable for guiding light bundles of pixels of the generated image, which are coupled into the spectacle lens via the coupling-in section of the spectacle lens, in the spectacle lens to the coupling-out section to couple them out of the spectacle lens via the coupling-out section. The coupling-out section includes at least two deflecting surfaces arranged next to each other which reflect the light bundles in the direction of the rear side for the coupling out. Deflecting surfaces can be formed as a switchable layer which can be switched into a first and a second state, wherein the reflectivity of the switchable layers in the first state is higher than in the second state.

PRIORITY

This application claims the benefit of German Patent Application No.102014207490.8 filed on Apr. 17, 2014, which is hereby incorporatedherein by reference in its entirety.

FIELD

The present invention relates to a spectacle lens for a display devicethat can be fitted on the head of a user and generates an image, and adisplay device with such a spectacle lens.

BACKGROUND

Spectacle lenses often comprise, seen in top view onto the spectaclelens, a coupling-in section (e.g. in an edge area of the spectacle lens)and a coupling-out section (e.g. in a central area of the spectaclelens), wherein the spectacle lens is suitable for guiding light bundlesof pixels of the generated image, which are coupled into the spectaclelens via the coupling-in section of the spectacle lens, in a lightguiding channel to the coupling-out section, in order to couple them outof the spectacle lens via the coupling-out section. The coupling-outsection can comprise at least two deflecting surfaces arranged next toeach other which reflect the light bundles in the direction of the rearside for the coupling-out. Because of the reflecting effect of thesedeflecting surfaces, they are disruptive for the user in particular whenno image is being displayed. The reflectivity of the deflecting surfacesleads to them being clearly set apart visually from the surroundingspectacle lens.

SUMMARY

An object of the invention is to provide a spectacle lens for a displaydevice that can be fitted on the head of a user and generate an image,which is developed in such a way that the difficulty named above can beovercome as completely as possible.

The disclosure includes a spectacle lens in which the deflectingsurfaces are in each case formed as a switchable layer which can beswitched into a first and a second state, wherein the reflectivity ofthe switchable layers in the first state is higher than in the secondstate. In particular, the transmissivity in the second state is higherthan in the first state.

Because of the switchable layer, which can also be referred to asswitchable mirror layer, it is advantageously possible to switch thecorresponding deflecting surfaces to be a reflecting surface only attimes in which the function of deflecting is required. If, e.g., noimage representation is desired, the switchable layer can be switchedinto the second state and thus into transmission. In the case of imagerepresentation, the switchable layer can be switched into the firststate only at times, for example, with the result that the reducedtransmittance is not disruptive for the user.

The deflecting surfaces can be formed in the spectacle lens. Inparticular, they can lie on the front side in the spectacle lens or bespaced apart from the front side. In particular, they can be formed suchthat the front side has its predetermined surface profile and has noother structuring on the surface because of the deflecting surfaces.

The switchable layer of the deflecting surfaces can comprise a liquidcrystal layer or an electrochromic layer. In particular, the switchablelayer can be formed as an electrically switchable layer.

At least two deflecting surfaces can be arranged next to each other canbe switched into the first and second state independently of each other.

The spectacle lens can comprise at least two groups arranged next toeach other with in each case at least two deflecting surfaces arrangednext to each other, wherein the deflecting surfaces in each case areformed as a switchable layer and the switchable layers of one of thegroups can be switched into the first and second state independently ofthe switchable layers of another group.

The spectacle lens can thus be used variably. For example, a largereyebox can thus be provided. Furthermore, it is possible to enlarge thefield of view or provide fields of view for different directions ofview. In order to achieve this, it can be necessary, in addition to thecorresponding actuation of the deflecting surfaces, to form thedeflecting surfaces oriented appropriately.

The deflecting surfaces can be formed flat or curved. Furthermore, thedeflecting surfaces can reproduce a curved reflecting surface in aFresnel manner which has an imaging property in addition to a pure beamdeflection.

The spectacle lens according to the invention can be formed as aspectacle lens with a single shell. However, it is also possible for itto be formed with two shells or more.

The switchable layer can be formed as an optically switchable layer. Itcan be formed as a passively switchable layer or as an activelyswitchable layer. By a passively switchable layer is meant in particulara layer which is switched into the first state by the light bundles ofthe pixels of the generated image itself. By an actively switchablelayer is meant in particular a layer which is switched into the first orsecond state by means of an additional radiation.

The front side and/or rear side of the spectacle lens can comprise aswitchable transmission layer. In particular, the switchabletransmission layer can be formed on the entire front side and/or on theentire rear side.

The transmittance of the switchable transmission layer can be set andaltered. This can be used e.g. in order to set the ratio of brightnessof the generated image to the ambient brightness. In particular, theswitchable transmission layer can be an electrically switchabletransmission layer. It can be formed for example as an electrochromiclayer.

The switchable transmission layer can, in particular, be formed in thesame way as the switchable layer for the deflecting surfaces.

The coupling-in section can be formed in an edge area of the spectaclelens and the coupling-out section can be formed in a central area of thespectacle lens.

Furthermore, the disclosure includes a display device, including aholder that can be fitted on the head of a user, an image-generatingmodule secured to the holder, which generates an image, and an imagingoptical system secured to the holder, which comprises a spectacle lensaccording to the invention and which, when fitted on the head, imagesthe generated image such that the user can perceive it as a virtualimage.

The imaging optical system can comprise the spectacle lens as the onlyoptical element. However, it is also possible for the imaging opticalsystem to comprise, in addition to the spectacle lens, also at least onefurther optical element. In particular, the spectacle lens can be formedin one piece together with the at least one further optical element.

Thus, the further optical element can be, e.g., a collimation opticalsystem which is arranged between the spectacle lens and theimage-generating module, with the result that the light bundles from theimage-generating module are coupled into the spectacle lens ascollimated bundles.

Furthermore, the display device can comprise a control unit whichactuates the switchable layer of the reflecting surface and optionallythe switchable second layer of the deflecting surfaces.

The control unit can actuate the switchable layers of the deflectingsurfaces such that the deflecting surfaces reflect the light bundlestowards the rear side one after the other over time.

In particular, the control unit can actuate the deflecting surfaces suchthat the field of view is maximized for the user.

The image-generating module can in particular comprise a two-dimensionalimaging system, such as e.g. an LCD module, LCoS module, an OLED moduleor a tilting mirror matrix. The imaging system can be self-luminous ornot self-luminous.

The image-generating module can in particular be formed such that itgenerates a monochromatic or a multi-coloured image.

The display device according to the invention can comprise furtherelements known to a person skilled in the art which are necessary forits operation.

It is understood that the features named above and those yet to beexplained below can be used not only in the stated combinations but alsoin other combinations or alone, without departing from the scope of thepresent invention.

FIG. 1 is a schematic perspective representation of an embodiment of thedisplay device according an example embodiment of the invention;

FIG. 2 is an enlarged partial sectional view of the first spectacle lensfrom FIG. 1;

FIG. 3 is a top view of the rear side of the first spectacle lens;

FIG. 4 is an enlarged partial sectional view of the first spectacle lensaccording to a further example embodiment;

FIG. 5 is an enlarged partial sectional view of the first spectacle lensaccording to a further example embodiment;

FIG. 6 is an enlarged partial sectional view of the first spectacle lensaccording to a further example embodiment;

FIG. 7 is an enlarged partial sectional view of the first spectacle lensaccording to a further example embodiment;

FIG. 8 is an enlarged partial sectional view of the first spectacle lensaccording to a further example embodiment;

FIG. 9 is an enlarged partial sectional view of the first spectacle lensaccording to a further example embodiment;

FIG. 10 is a top view onto the rear side of the first spectacle lensaccording to the embodiment from FIG. 9;

FIG. 11 is an enlarged partial sectional view of the first spectaclelens according to a further example embodiment;

FIG. 12 is an enlarged partial sectional view of the first spectaclelens according to a further example embodiment;

FIG. 13 is an enlarged partial sectional view of the first spectaclelens according to a further example embodiment;

FIG. 14 is an enlarged partial sectional view of the first spectaclelens according to a further example embodiment;

FIG. 15 is an enlarged partial sectional view of the first spectaclelens according to a further example embodiment,

FIG. 16 is an enlarged partial sectional view of the first spectaclelens according to a further example embodiment;

FIG. 17 is an enlarged representation to explain the layer structure ofthe electrically switchable reflecting surface;

FIG. 18 is a sectional view to explain the layer structure of thereflective facets;

FIG. 19 is a sectional view to explain the layer structure of theelectrically switchable reflecting surface;

FIG. 20 is a sectional view to explain the layer structure of thereflective facets;

FIG. 21 is a sectional view to explain a further layer structure of anembodiment of the reflective facets;

FIG. 22 is a top view to explain the contacting of the reflective facetsaccording to FIG. 21;

FIG. 23 is a schematic representation to explain the actuation of theelectrically switchable reflective layers, the electrically actuatablereflective facets and the imaging system;

FIGS. 24A-24D are representations to explain the settable duty factorsof the electrically switchable reflective layers and the reflectivefacets;

FIG. 25 is a schematic representation to explain the intensity of thelight of the image-generating module in comparison with the ambientlight as a function of time;

FIG. 26 is an enlarged partial sectional view of the first spectaclelens according to a further embodiment, and

FIG. 27 is an enlarged partial sectional view of the first spectaclelens according to a further embodiment.

While the invention is amenable to various modifications and alternativeforms, specifics thereof have been shown by way of example in thedrawings and will be described in detail. It should be understood,however, that the intention is not to limit the invention to theparticular example embodiments described. On the contrary, the inventionis to cover all modifications, equivalents, and alternatives fallingwithin the scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION

In the following descriptions, the present invention will be explainedwith reference to various exemplary embodiments. Nevertheless, theseembodiments are not intended to limit the present invention to anyspecific example, environment, application, or particular implementationdescribed herein. Therefore, descriptions of these example embodimentsare only provided for purpose of illustration rather than to limit thepresent invention.

In the embodiment shown in FIG. 1, the display device 1 according to theinvention comprises a holder 2 that can be fitted on the head of a userand is formed in the case of the embodiment described here as aconventional spectacles frame, as well as a first and a second spectaclelens 3, 4, which are secured to the holder 2. The holder 2 with thespectacle lenses 3 and 4 can be formed e.g. as sports glasses,sunglasses and/or glasses for correcting defective vision, wherein avirtual image can be reflected into the user's field of view via thefirst spectacle lens 3, as is described below.

The spectacle lenses 3, 4, and in particular the first spectacle lens 3,are only described together with the display device 1 according to theinvention by way of example. The spectacle lenses 3, 4, or at least thefirst spectacle lens 3, are in each case formed individually as aspectacle lens according to the invention. The second spectacle lens 4can, of course, (additionally or alternatively) be formed in the samemanner as the first spectacle lens 3 which is yet to be described below.

As can best be seen from the enlarged partial sectional view in FIG. 2,the display device 1 comprises an image-generating module 5, whichcomprises an imaging system 6 (e.g. an OLED module) with which an imagecan be generated that is to be reflected into the user's field of viewas the virtual image. For this, the display device 1 comprises animaging optical system 7 which contains an optical element 8 arrangedbetween the imaging system 6 and the first spectacle lens 3. Inaddition, the first spectacle lens 3 itself also serves as part of theimaging optical system 7.

The imaging system 6 is formed as a two-dimensional imaging system witha plurality of pixels arranged e.g. in columns and rows, wherein a lightbundle 9 can emerge from each pixel. The desired image can be generatedby correspondingly actuating the pixels. In FIG. 2, the beam path of alight beam is drawn in to represent the light bundles 9, with the resultthat the light beam 9 is also discussed below.

The light beam 9 emerging from the imaging system 6 enters the opticalelement 8 via an entry surface F1 of the optical element 8 and exits theoptical element 8 via an exit surface F2 which is formed curved. Thelight beam 9 then enters the first spectacle lens 3 via an entry surfaceF3 which is formed curved on the end face 10 of the first spectacle lens3 and strikes the front side 11 of the first spectacle lens at such anangle that a total internal reflection takes place. Through a furthertotal internal reflection on a rear side 14 of the first spectacle lens3 (more than the two total internal reflections shown can take place),the light beam 9 is guided to a coupling-out section 13, at which thelight beam 9 is reflected to the rear side 14 of the first spectaclelens 3 such that it exits the first spectacle lens 3 via the rear side14. In order to bring about this deflection in the coupling-out section13, several reflective facets 15, or reflective surfaces, are arrangednext to each other.

Thus, when a user is wearing the display device 1 according to theinvention on his head as intended, he can perceive the image generatedby means of the imaging system 6 as a virtual image when he looks at thecoupling-out section 13. In the embodiment described here, the user mustlook slightly towards the right relative to the direction of view G of aforward view. In FIG. 2, the centre of rotation 17 of the user's eye andthe eyebox 18 (the area which is provided by the display device 1 and inwhich the user's eye can move and he can still see the generated imageas a virtual image) is drawn in for clarification. The eyebox 18 canalso be referred to as exit pupil 19 of the imaging optical system 7.

The section of the first spectacle lens 3 via which the light beam 9 iscoupled into the spectacle lens 3 can be referred to as coupling-insection 19, with the result that the section of the rear side 14 onwhich the total internal reflection takes place serves, together withthe section of the front side 1 on which the total internal reflectiontakes place, as light guiding channel 20, which guides the beams 9coupled in via the coupling-in section 19 to the coupling-out section13. The arrangement of the two sections 13 and 19 and the light guidingchannel 20 can be easily recognized in FIG. 3.

Each reflective facet 15 is formed as electrically switchable reflectingsurface and can thus also be referred to as electrically switchablefacet 15. The electrically switchable facets 15 can be switched into afirst and into a second state.

This can e.g. be carried out simultaneously or also individually foreach facet 15. The reflectivity in the first state is higher than in thesecond state and the transmissivity in the second state is higher thanin the first state. The electrically switchable facets 15 can thus beswitched into a reflection state (first state) or a transmission state(second state).

When the reflective facets 15 are switched into the first state, thelight beam 9 is reflected towards the rear side 14 and coupled out viait. To control the electrically switchable facets 15, the display device1 comprises a control unit 21, which can switch the electricallyswitchable facets into the first and second state. In FIG. 2, acorresponding control line L2 is also drawn in schematically.

The control unit 21 can switch the reflective facets 15 so quickly backand forth between the two states for example that a user can no longerresolve the individual switchover processes over time. This occurs fromabout 30 Hz, with the result that the user can then only still perceivethe transmission averaged over time in the area of the light guidingchannel 20. On the simplified assumption that in the first state thereflectivity is 100% and in the second state the reflectivity is 0%, theuser would be able to perceive a reflectivity of 50% if the reflectivefacets 15 are in the first state for half the time of a predeterminedduration and in the second state for the remaining time of thepredetermined duration (disregarding the actual duration of theswitchover). In this case, the transmissivity would also be 50%, withthe result that the user would perceive the surroundings with a lowerbrightness in the area of the coupling-out section 13.

Of course, a different reflectivity or transmissivity of the reflectivefacets 15 can also be set. In principle it is possible to set thereflectivity freely in the range of from 0%-100% and thus thetransmissivity in the range of from 100%-0%. This depends essentiallyonly on the ratio of the duration of the first state to the duration ofthe second state.

Preferably, the actuation of the reflective facets 15 can besynchronized with the image generation by means of the imaging system 6.Dark phases can thus occur during the image generation, during which noimage generation takes place. In these dark phases, the reflectivefacets 15 can be switched into the second state. During the other phasesof the image generation, the reflective facets 15 are switched into thefirst state at least at times.

At times when no image is to be generated, the reflective facets 15 canbe switched into the second state, with the result that the user canthen detect no difference in the area of the coupling-out section 13from the remainder of the first spectacle lens 3.

The synchronous actuation of the reflective facets 15 and of the imagingsystem 6 can thus be carried out such that the facets 15 are alwaysswitched into the first state when the imaging system is in ON mode. Inthe first state, the reflective facets 15 have the desired reflectivity,with the result that the coupling-out of the light beams 9 can becarried out in the desired manner.

When the imaging system 6 is in OFF mode, and thus is not generating animage, the reflective facets 15 can be switched into the second state.No reflection thus takes place on the reflective facets, as they are intransmission mode.

Each reflective facet 15 is formed as electrically switchable reflectingsurface which is actuated by means of the control unit 21 via thecontrol line L2 represented schematically in FIGS. 2 and 3.

The reflective facets 15 can bring about a pure beam deflection or canin addition also have an imaging property. The facets 15 themselves canbe formed flat or curved. In particular, the facets 15 can reproduce ina Fresnel manner a curved reflecting surface which has the desireddeflection and optionally imaging properties.

The embodiment shown in FIG. 4 differs from the embodiment from FIG. 2essentially only in the positioning of the reflective facets 15. In theembodiment according to FIG. 4, the facets 15 are positioned on thefront side 11 of the spectacle lens 3 such that the generated image canbe perceived by the user in forward view.

In FIG. 5, a modification is shown in which a first group 25 ofswitchable reflective facets 15 and next to that a second group 26 ofswitchable reflective facets 15 are provided. The switchable reflectivefacets 15 are actuated via control lines L2 and L3 such that those ofthe first group 25 are switched into the first and second state in eachcase alternately to those of the second group 26. An enlargement of theeyebox 18 can thus be achieved in a simple manner, as the light beams 9,when the facets 15 of the first group 25 are switched into the secondstate, are guided by total reflection on the front side 11 and on therear side 14 to the second group 26 of the reflective facets 15 and canthen be reflected in the direction of the rear side 14 by these for thecoupling-out, with the result that the desired enlarged eyebox 18 ispresent.

In FIG. 6, a modification of the display device 1 according to theinvention is shown, in which three groups 25, 26, 27 of electricallyswitchable reflective facets 15 are arranged next to each other, whichare actuated by means of the control unit 21 via control lines L2, L3,L4 such that the light beams 9 in each case are coupled out by thereflective facets of one of the groups 25 to 27 one after the other.This leads to an enlarged field of view.

Of course, the reflective facets 15 can also be buried in the spectaclelens such that they are spaced apart from the front side 11, as is shownin FIG. 7.

In FIG. 8, a modification is shown in which two groups 25, 26 ofelectrically switchable reflective facets 15 are provided, wherein thetwo groups 25 and 26 are spaced so far apart from each other that theuser is provided with two fields of view (one in forward view and one ina view towards the right). Of these two groups 25, 26, e.g. one can beselected in order to bring about the image coupling-out in the desiredfield of view.

In FIG. 9, a further modification of the display device 1 according tothe invention is shown in which, in turn, two groups 25, 26 ofelectrically switchable, reflective facets are provided. The controlunit 21 actuates the facets of the two groups 25, 26 such that alwaysonly the facets 15 of one of the two groups 25, 26 serve for thecoupling-out. It is thus possible to adapt the coupling-out section 13to the pupil position. Thus, for example, anatomical differences betweendifferent users can be compensated for, such as e.g. the differentdistance between the temple and the eye of the respective user.

In FIG. 10, a top view of the corresponding spectacle lens from FIG. 9is shown. It can be easily recognized there that the two groups 25, 26of facets 17 are spaced apart from each other.

In FIG. 11, an embodiment of the spectacle lens 3 according to theinvention is shown in which an electrically switchable reflectingsurface 12 is formed in the first spectacle lens 3. For clarification, acircular line K is drawn in which, however, is not present in the actualspectacle lens 3. The reflecting surface 12 is formed flat and can beswitched into a first and a second state, wherein the reflectivity inthe first state is higher than in the second state, in the same manneras the electrically switchable facets 15. For this, the reflectingsurface 12 is connected to the control unit 21 via a line L1. In thisembodiment, the guiding of the light bundles takes place through totalinternal reflection on the front side 14 and reflection on thereflecting surface 12. Thus, the reflecting surface 12 together with thecorresponding section of the front side 11 forms the light guidingchannel 20, which guides the beams 9 coupled in via the coupling-insection 19 to the coupling-out section 13.

The reflecting surface 12 can be actuated in the same manner as thereflective facets. In particular, the actuation of the reflectingsurface 12 can be synchronized with the image generation by means of theimaging system 6. Dark phases can thus occur during the imagegeneration, during which no image generation takes place. In these darkphases, the reflecting surface 12 can be switched into the second state.During the other phases of the image generation, the reflecting surface12 is switched into the first state at least at times. At times when noimage is to be generated, the reflecting surface 12 can be switched intothe second state, with the result that the user can then detect nodifference in the area of the light guiding channel 20 from theremainder of the first spectacle lens.

In principle, the reflectivity of the reflecting surface 12 can befreely set in the range of from 0% to 100%. Then, a transmissivity inthe range of from 100% to 0% is thus present. The set reflectivity andthus also the set transmissivity depends essentially only on the ratioof the duration of the first state to the duration of the second state.

In the embodiment according to FIG. 11, the reflecting surface 12 isformed as a flat continuous surface. However, it is also possible todivide the surface into flat partial sections 12 ₁, 12 ₂, 12 ₃ and toarrange the curvature of the spectacle lens correspondingly like steps,as is shown in FIG. 12. Furthermore, in the embodiment from FIG. 12,unlike the embodiment according to FIG. 11, the reflection no longertakes place on the front side 11, as a second electrically switchablereflecting surface 22 is formed which is opposite the first reflectingsurface 12 and comprises partial sections 22 ₁, 22 ₂, 22 ₃ which areoffset like steps in the same manner. To simplify the representation,the control line for the second reflecting surface 22 is not drawn inFIG. 12. Between the two reflecting surfaces 12 and 22, a material isfilled in which corresponds, for example, to the material of the firstspectacle lens 3. Furthermore, in the embodiment according to FIG. 12,the reflective facets 15 are not formed on the front side 11, but ratherare buried in the spectacle lens 3.

The actuation of the two reflecting surfaces 12 and 22 and of thereflective facets 15 takes place, in turn, via the control unit 21 in asynchronous manner with each other and also preferably synchronouslywith the imaging system 6.

The embodiment according to FIG. 13 differs from the embodimentaccording to FIG. 12 only in that no material is filled in between thetwo reflecting surfaces 12 and 22, but rather there is a cavity and airis thus present.

In FIG. 14, a further modification of the embodiment according to FIG.12 is shown, wherein in this case the two reflecting surfaces 12 and 22are formed as continuous flat surfaces. The area between the tworeflecting surfaces 12 and 22 can be filled with material (e.g. the samematerial as that of the first spectacle lens) or be formed as a cavity(e.g. filled with air). The light guiding channel 20 can thus bedesigned by choosing the material according to the optical frameworkconditions present.

In the embodiment shown in FIG. 15, the light guiding channel 20 isformed by the switchable reflecting surface 12 and the opposite sectionof the rear side 14 of the spectacle lens. Furthermore, in thisembodiment the reflective facets 15 are arranged buried in the spectaclelens 3 such that they are spaced apart from the front side 11. Such aburied formation of the reflective facets 15 leads e.g. to thereflective facets 15 being well protected against environmental effects.

In FIG. 16, a modification of the embodiment according to FIG. 11 isrepresented. In this modification, a front spectacle lens element 30 anda rear spectacle lens element 31 are drawn in with dotted lines. In thiscase, the spectacle lens 3 has a three-shell structure. It is alsopossible for only one of the two spectacle lens elements 30, 31 to beprovided, with the result that a two-shell structure is then present.

If the front spectacle lens element 30 is provided, it must only beensured that the drawn-in reflection takes place on the front side 11,which is now inside the spectacle lens. This can be achieved e.g. byappropriately choosing the material for the front spectacle lenselement. Alternatively, a partially reflective coating, a switchablereflecting surface or similar can be provided.

This multi-shell formation of the spectacle lens 3 can be provided forall described embodiments.

The electrically switchable reflecting surface 12, 22 can be formed asan electrochromic layer. For this, for example, it can comprise, as isshown schematically in FIG. 17, a transparent conductive oxide layer 40,an electron layer 41, an ion conductive layer 42, an electron layer 43and a transparent conductive oxide layer 44 formed one on top of anotherin this sequence. Such a layer system can be switched from the firststate (reflection state) into the second state (transmission state) byapplying a predetermined voltage. A switchable mirror surface is thuspresent.

Such electrochromic layer systems for forming switchable mirrors areknown to a person skilled in the art. For example, they can be formed asindicated in the article “New electrochromic mirror systems”, Thomas J.Richardson, Solid State Ionics 165 (2003) 305-308. It is also possibleto form the layer system such that it comprises a transparent electrode,a switchable mirror layer made of metal, a catalyst layer made of metal,an electrolyte adhesive layer, an ion storage layer (oxide layer) and atransparent electrode stacked one on top of another in this sequence, asis described e.g. in the press release, published on the Internet, ofthe National Institute of Advanced Industrial Science and Technology ofJapan with the title “High-efficiency Fabrication Technology forSwitchable Mirror Devices Capable of Switching between Mirror andTransparent States”.

As is shown in FIG. 18, the reflective facets 15 can also comprise thesame layer structure as is indicated in connection with FIG. 17 for theswitchable reflecting surface 12, 22.

It is further possible to form the switchable reflecting surface 12, 22as a liquid crystal layer system, as is represented schematically inFIG. 19. This layer system comprises an analysis layer 50, a transparentconductive oxide layer 51, a liquid crystal layer 52, a transparentconductive oxide layer 53 and a polarizing layer 54, stacked one on topof another in this sequence. Such a layer system can also be switchedback and forth between a reflection state and a transmission state byapplying a voltage. The polarizing and analysis layers 54, 50 areoptional and can also be omitted.

Such layer systems are also known to a person skilled in the art.Reference is made purely by way of example to U.S. Pat. No. 6,674,504 B1and DE 10 2009 057 987 A1, in which specific designs of such layersystems are indicated.

The liquid crystal layer system can also be used for the reflectivefacets 15, as is represented schematically in FIG. 20.

A modification of the embodiment from FIG. 20 is shown in FIG. 21. Inthis modification, the reflective facets 15 are spaced apart from eachother and in each case flat intermediate pieces 55 are provided. Theintermediate pieces 55 can in each case be arranged e.g. parallel to thetangent of the front side 11 at a point directly above the correspondingintermediate piece 55 or at an angle relative to this. Furthermore, theoverall thickness of the layer structure is clearly reduced, as isrepresented schematically in FIG. 21.

Furthermore, in the embodiment according to FIG. 21, each facet 15 canbe actuated individually. For this, on the upper side of the flatintermediate piece 55, a first contacting surface 56 is formed, which isconnected to a transparent strip conductor 57, as is indicated in theschematic top view from FIG. 22. Due to the flat design of theintermediate piece 55, the contacting is possible in a simple manner.Furthermore, the underside of the flat intermediate piece 55 is providedwith a second contacting surface 58 which is connected to a transparentstrip conductor 59. This type of contacting is represented in theschematic top view from FIG. 22, wherein here only the contactingsurfaces 56 and 58 as well as the transparent strip conductors 57 and 59are represented schematically. The transparent strip conductors 57, 59are guided to the control unit 21.

Through this type of contacting, each reflective facet 15 can beactuated individually. Production in a method using layers is alsoeasily possible.

The layer structure of the reflective facets 15 can (but does not haveto) extend in the area of the flat intermediate piece 55, or can thusform the flat intermediate piece 55.

In the representation shown in FIG. 22, the contacting surfaces 56 and58 extend in each case only approximately to the centre of the flatintermediate pieces 55 when seen in a direction from top to bottom inFIG. 22. Of course, they can also extend over the entire length of theflat intermediate pieces 55 in this direction.

The electrically switchable reflecting surface 12, 22 and/or theactuatable electrically switchable reflective facets 15 can inparticular also be actuated such that the image brightness of thegenerated image is thus controlled or regulated. This can be carriedout, e.g., in dependence on the ambient brightness. Thus, the reflectingsurface 12, 22 and/or the reflective facets 15 can be actuated such thatthey transmit the maximum image brightness or an image brightness thatis less than the maximum. In this manner, a control or regulation of theimage brightness and/or of the brightness contrast (image brightness toambient brightness) can be carried out in a simple manner.

To control or regulate the brightness contrast, an electrochromic layer,which can likewise be actuated by means of the control unit 21, can bearranged over the whole surface on the front side 11 of the firstspectacle lens 3. In this case, it is possible to dim the transmissionof the first spectacle lens and thus set the desired brightnesscontrast.

As has already been described, the electrically switchable reflectingsurfaces 12, 22 and the electrically switchable reflective facets 15 canbe switched back and forth between a first and a second state, whereinthe reflectivity in the first state is higher than in the second state.Thus, e.g., for simplification it can be assumed that the reflectivityis 100% in the first state and 0% in the second state. The control unit21 can ensure that the imaging system 6 on the one hand and thecorrespondingly switchable layers 11, 22, or facets 15, on the otherhand are actuated synchronously. For this, the control unit 21 canactuate a corresponding imaging system actuation 60, which is suppliedwith video data 61 and which actuates the imaging system 6, and acorresponding layer actuation 62, which actuates the reflective layers12, 22 and the reflective facets 15, such that these are synchronized.The corresponding actuation is represented schematically in FIG. 23.

The actuation by means of the control unit 21 can now take place suchthat the switching back and forth between the two states is carried outat a frequency of 30 Hz or more. In this case, a user can only stillperceive the reflection or transmission of these layers 12, 22, or ofthe reflective facets 15 averaged over time.

By setting the duty factor (thus the ratio of the duration of the firststate to the second state), each desired reflection can thus be set in asimple manner.

In the schematic representation shown in FIG. 24A, the duty factor is25%. This means that for 25% of the time t the reflective layers 12, 22and/or the reflective facets 15 are in the first state (100%reflectivity) and for the remaining time they are in the second state(the switchover time is disregarded for simplification). The first statecan also be referred to as the ON state, and the second state can alsobe referred to as the OFF state.

The reflectivity is thus 25% of the maximum reflectivity and thetransmittance is 75% of the maximum transmittance.

In the duty factor represented in FIG. 24B, the reflectivity is 50% ofthe maximum reflectivity. In FIG. 24C and FIG. 24D, duty factors for areflectivity of approx. 66.6% and 75% of the maximum reflectivity areshown.

In the embodiments described up to now, the facets 15 and the reflectingsurfaces 12 and 22 are in each case formed such that they areelectrically switchable. However, it is also possible to form thesesurfaces as optically switchable surfaces 15, 12 and 22. For this, forexample, it is possible to exploit the fact that the light coming fromthe image-generating module 5 (light beams 9) is time-modulated and thushas a higher intensity, at least intermittently, than the ambient light,as is represented schematically in FIG. 25.

In FIG. 25, the intensity I is plotted against the time t, wherein thelight of the image-generating module 5 is indicated with the referencenumber 63 and the ambient light is indicated with the reference number64. The representation in FIG. 25 is purely schematic. Thus, theintensity of the light of the image-generating module 5 can in realitybe more than one order of magnitude higher than the intensity of theambient light.

This difference in the intensity can e.g. be used in such a way that amaterial with non-linear electric susceptibility is used as reflectinglayer or reflecting coating.

This is shown schematically in the sectional view according to FIG. 26,wherein here the coupling-out section 13 comprises a single continuouslayer 65. However, this is meant only by way of example. Of course, inthe same manner, the already described facets 15, the reflecting surface12 and/or the reflecting surface 22 can comprise a layer or coating madefrom such a material with non-linear electric susceptibility.

For example, lithium niobate (LiNbO₃) can be used as the material, thecorresponding coefficient d₃₃ of which, along the axis with thestrongest non-linearity, has a value of about 30 pm/V according to thefollowing formulaP=2·ϵ₀ ·d ₃₃ ·E ²

In this formula, P is the polarization, ϵ₀ the absolute permittivity andE the electrical field strength. Ultimately this means that the electricsusceptibility χ_(e), which is defined according to the followingformula{right arrow over (P)}=ϵ ₀·χ_(e) ·{right arrow over (E)}

becomes dependent on the field strength. The refractive index n thusbecomes, according to the following formula,n=√{square root over (1+χ_(e))}

also dependent on the field strength, wherein this formula applies inthe case that the material is not magnetic. From the known Fresnelformulae, the field strength-dependent reflectivity can then bedetermined.

Thus, the layer 65 has a higher reflectivity for the light 9 of theimage-generating module 5 than for the ambient light, with the resultthat the surface 65 is optically switched. A passive optical switchingis effectively present, as the light of the image-generating module 5itself brings about the switchover of the layer 65.

Furthermore, it is possible to form the surface 65 from aphotorefractive material which changes its refractive index for acertain time under illumination. Such photorefractive materials are e.g.BaTiO₃, KNbO₃ and LiNbO₃. The change in the refractive index, inaccordance with the Fresnel formulae, in turn leads to a change in thereflectivity. Depending on the refractive index of the surroundingmaterial (higher or lower than that of the photoreactive material), anincrease or decrease in the reflectivity can be achieved as theintensity grows.

Coatings can also be used which reflect or are transparent depending onthe brightness. For instance, the company Schott A G from Mainz inGermany markets, under the product name Mirona, a mirror which loses itsreflectivity and becomes transparent when it is bright behind themirror. If it is dark behind the mirror, it is reflective.

Such coatings can be formed such that the switchover effect betweenreflection and transmission is brought about by radiation in the UVrange or from the infrared range. In this case it is possible, by meansof an auxiliary radiation source 66, as is represented schematically inFIG. 27, to switch the reflective layer 65 back and forth betweenreflection and transmission. An optical layer is thus present which isactively switchable. If the radiation 67 of the auxiliary radiationsource 66 is required to generate the transmissive state of thereflective layer 65, the auxiliary radiation source 66 must thus beswitched on during the time in which no image generation by means of theimage-generating module 5 is taking place. When an image is beinggenerated by means of the image-generating module 5, the auxiliaryradiation source 66 is to be switched off.

In the reverse case, if the layer 65 is brought into the reflectivestate by illumination by means of the radiation 67 of the auxiliaryradiation source 66, the auxiliary radiation source 66 must always beswitched on when an image is being generated by means of theimage-generating module 5.

On the front side 11 of the spectacle lens 3, a filter layer 68 isapplied, which filters the wavelength from the ambient light whichcorresponds to the wavelength of the auxiliary radiation 67. The layer68 is thus designed for example such that UV radiation and/or infraredradiation is filtered out.

If UV radiation or radiation of another wavelength which can be harmfulto the eye is used as auxiliary radiation 67, an absorber layer 69 whichabsorbs the auxiliary radiation is formed on the inside 14, with theresult that the auxiliary radiation can be reliably prevented fromentering the eye.

In the described embodiments of the display device 1 according to theinvention the reflection of the virtual image into the user's field ofview takes place via the first spectacle lens 3. Of course, a reflectionvia the second spectacle lens 4 is also possible. In addition, thedisplay device 1 can be formed such that items of information or virtualimages are reflected via both spectacle lenses 3, 4. The reflection cantake place such that a three-dimensional image impression results.However, this is not absolutely necessary.

The spectacle lenses 3, 4 can have a refractive power of zero or arefractive power different from zero (in particular to correct visiondefects). As is shown in the figures, both the front side 11 and therear side 14 of the spectacle lens 3 are formed curved. In particular,the front side 11 can be spherically curved. If the spectacle lens has arefractive power different from zero, in order to correct defectivevision, as a rule the curvature of the rear side 14 is chosenappropriately, in order to achieve the desired correction.

The holder 2 does not have to be formed as a spectacles-type holder. Anyother type of holder with which the display device 1 can be fitted orworn on the head of the user is also possible.

The features of the described embodiment examples can, insofar as it istechnically meaningful, be combined with each other in order to providefurther embodiments of the display device according to the invention.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiments,it will be apparent to those of ordinary skill in the art that theinvention is not to be limited to the disclosed embodiments. It will bereadily apparent to those of ordinary skill in the art that manymodifications and equivalent arrangements can be made thereof withoutdeparting from the spirit and scope of the present disclosure, suchscope to be accorded the broadest interpretation of the appended claimsso as to encompass all equivalent structures and products. Moreover,features or aspects of various example embodiments may be mixed andmatched (even if such combination is not explicitly described herein)without departing from the scope of the invention.

The invention claimed is:
 1. A spectacle lens for a display device thatcan be fitted on the head of a user and generate an image, the spectaclelens formed of a material, the spectacle lens comprising: a coupling-insection where light bundles of pixels of the image are coupled into thematerial of the spectacle lens; a coupling-out section where lightbundles of pixels of the image are coupled out of the material of thespectacle lens; a front side; a rear side, wherein at least one of thefront side and the rear side is curved; and a light guiding channelconfigured to guide the light bundles of pixels of the image within thematerial from the coupling-in section to the coupling-out section,wherein the coupling-out section comprises at least two deflectingsurfaces arranged next to each other which are configured to reflect thelight bundles in the direction of the rear side for the coupling-out,and wherein the deflecting surfaces are each configured as a switchablelayer which can be switched into a first and a second state, wherein thereflectivity of the switchable layers in the first state is higher thanin the second state.
 2. The spectacle lens according to claim 1, whereinthe at least two deflecting surfaces arranged next to each other areconfigured to be switched into the first and second state independentlyof each other.
 3. The spectacle lens according to claim 1, wherein thecoupling-out section comprises two groups arranged next to each otherwith, in each case, at least two deflecting surfaces arranged next toeach other, wherein the deflecting surfaces in each case are formed asthe switchable layer and the switchable layers of one of the two groupscan be switched into the first and second state independently of theswitchable layers of the other of the two groups.
 4. The spectacle lensaccording to claim 1, wherein the deflecting surfaces are configured toreproduce a curved reflecting surface in a Fresnel manner, whichincludes an imaging property in addition to a pure beam deflection. 5.The spectacle lens according to claim 4, wherein the deflecting surfacesare flat.
 6. The spectacle lens according to claim 1, wherein thedeflecting surfaces are flat.
 7. The spectacle lens according to claim1, wherein the deflecting surfaces are curved.
 8. The spectacle lensaccording to claim 1, wherein the deflecting surfaces each comprise anelectrically switchable layer.
 9. The spectacle lens according to claim1, wherein the deflecting surfaces each comprise an optically switchablelayer.
 10. The spectacle lens according to claim 9, wherein theoptically switchable layer comprises a passively switchable layer. 11.The spectacle lens according to claim 9, wherein the opticallyswitchable layer comprises an actively switchable layer.
 12. Thespectacle lens according to claim 1, wherein on at least one of thefront side and the rear side a switchable transmission layer is formed,wherein the transmittance of the switchable transmission layer issettable.
 13. The spectacle lens according to claim 12, wherein theswitchable transmission layer comprises an electrically switchabletransmission layer.
 14. The spectacle lens according to claim 12,wherein the switchable transmission layer comprises an opticallyswitchable transmission layer.
 15. A display device, comprising: aholder that can be fitted on the head of a user; an image-generatingmodule secured to the holder, which can generate an image; an imagingoptical system secured to the holder, the imaging optical systemcomprising a spectacle lens according to claim 1 and which, when theholder is fitted on the head, images the generated image such that theuser can perceive it as a virtual image; and a control unit configuredto actuate the switchable layers of the deflecting surfaces.
 16. Thedisplay device according to claim 15, wherein the control unit isfurther configured to actuate the switchable layers of the deflectingsurfaces such that the deflecting surfaces reflect the light bundlestowards the rear side one after the other over time.
 17. The displaydevice according to claim 16, wherein the control unit is furtherconfigured to actuate the deflecting surfaces such that the field ofview is maximized.